Seat Bulkhead

The panels for the seat are not quite enough by themselves to distribute the forces of one pedaling at full tilt. In addition, it is difficult to make sure the seat panels are properly positioned with respect to each other and the deck.

Part of the solution is to make an internal horizontal bulkhead. This will help transfer forces from the seat back to the side and rear panels. It will also help keep the panels from falling inward when the panel edges are glued together with thickened resin.


Since the shape is a bit irregular, I made a paper skirt. While there are probably a dozen other ways to do it, I did it this way.
1. Get a dozen 8-1/2 by 11 inch sheets of paper, an adhesive tape dispenser and a small level
2. Take two sheets of paper, butt them together along the long edge, and apply tape to the two pieces so that you now have a 17 x 11 inch piece of paper.
3. Using the level to make sure the edge of the paper is level, center and tape the long edge of this 17x11 sheet of paper to the seat back about half way up. Don't use more than one or two small pieces of tape for this.
4. While holding the sheet horizontal, take the level to one of the adjacent side panels of the seat and hold one end at the same height where the sheet intersects the side of the seat back.
5. Take another sheet, center and tape it to the side panel so that the long edge is at the same level as the edge of the paper on the seat back.
6. Hold both the 17x11 sheet and the new 8-1/2x11 sheet horizontal. The end of one sheet should overlap the end of the other sheet.
7. Tape the overlapping ends together, taking care to make sure the paper remains horizontal.

Repeat the process going around the seat panels until you arrive back at the seat back.

You should now have an irregular ring of paper, or skirt, that more or less is sticking out around the seat panels at the same height.


Carefully remove the skirt from the seat panels so that the shape is preserved.

You can either use the skirt as-is, or take more sheets of paper, tape them together, and trace the pentagonal hole onto them, and cut out the traced drawing. This makes a simple template for the bulkhead.


Note: Since the hole is taken from the outside of the seat panels, you will need to subtract the thickness of the panels from the outer edges of the template.


Take the template and use it to mark the shape of the bulkhead on whatever you plan to use for the bulkhead, and cut out the bulkhead.


I chose some scrap blue styrofoam insulation that I had laying about. As it turned out it was almost exactly the width of the inside of the seat. It was also nearly 2 inches thick, so the slant of the seat back and the rear-most panels needed to be taken into account.

Using a protractor level (Sears), I measured the seat back at about 60 degrees. The rear panels measured at about 7 degrees. The sides, being parallel, can be ignored.

Using the protractor level I tilted it to 60 degrees with one end at the lower corner of the foam and the upper end towards the interior of the foam. The template was placed at the intersection of the top of the foam and the level. A line was drawn across the foam along the edge of the template.


The triangular opposite end of the template was also traced on the foam at this time.

The foam was now cut. I used a bandsaw as it makes a very smooth, clean edge. It also has a nice tilting table marked in degrees, which made the 60 degree and 7 degree cuts very easy.